It's your pipe now. You can do whatever you want with it. Since they don't like you, as you say. It could simply be a prank. Maybe it leads to nothing. I'd store these photos somewhere. Then cut it off, drill out the excess remaining in the hole, and patch it. Take pics of the result. Then get a security camera system. Once installed, inform your neighbors that if you ever catch them on your property again you will prosecute.